Cleaner forms of storing energy are in great demand. Examples of clean energy storage include rechargeable lithium (Li) ion batteries i.e., Li-secondary batteries), in which Li+ ions move from a negative electrode to a positive electrode during discharge. In numerous applications (e.g., portable electronics and transportation), it would be advantageous to use a solid state Li ion battery which includes solid state materials such as solid state electrolytes as opposed to one that includes liquid components, (e.g., flammable liquid electrolytes). Using entirely solid state components improves battery safety and energy density, the latter of which is due in part to reduced electrode and electrolyte volume and weight.
Components of a solid state battery include the electrolyte, which electrically isolates the positive and negative electrodes, a catholyte, which is intimately mixed with a positive electrode active material to improve the ionic conductivity therein. A third component, in some Li ion batteries, is an anolyte which is laminated to, or in contact with, an anode material (i.e., negative electrode material; e.g., Li-metal). Currently available electrolyte, catholyte, and anolyte materials, however, are not stable within, or otherwise suitable for use with, solid state battery operating voltage ranges or when in contact with certain cathode or anode active materials such as lithium metal anodes.
Garnet (e.g., Li-stuffed garnet) is a class of oxides that has the potential to be suitable for use as one or more of a catholyte, an electrolyte, and an anolyte in a solid state battery. However, garnet materials have yet to be prepared with the proper morphology (e.g., thin film or nanostructured powder which can be sintered into sufficiently dense films or pellets), with sufficient conductivity or particle connectivity to function in commercial applications. Certain garnet materials and processing techniques are known (e.g., See U.S. Pat. Nos. 5,840,436; 8,658,317; 8,092,941; and 7,901,658; or U.S. Patent Application Publication Nos. 2013/0085055; 2011/0281175; 2014/0093785; 2014/0134483; 2015/0099190; 2014/0060723; 2009/0197172; 2010/00119800 and 2014/0170504; International Patent Application Publication Nos. WO 2010/0051345; 2010/096370 or also Bonderer, et al., Journal of the American Ceramic Society, 2010, 93(11):3624-3631; and Murugan, et al., Angew Chem. Int. Ed. 2007, 46, 7778-7781), but these materials and techniques suffer from a variety of deficiencies. The electrolyte films made by these techniques have insufficient Li+ ion conductivity and/or cycle life at high current density and/or low temperatures for use in commercial applications, and these techniques are not compatible with many battery components.
Accordingly, there is a need for improved methods of making and processing solid electrolytes such as sintered lithium-stuffed garnet electrolytes.